Amidate iridium(III) bis(2-pyridyl)phenyl complexes: Application examples of amidate ancillary ligands in iridium(III)-cyclometalated complexes

Article abstract of DOI:10.1021/om100714g

The syntheses, structures, and photophysical properties of a series of iridium(III) bis(2-pyridyl)phenyl complexes, (ppy)₂Ir(LX) (LX = amide ligands), are described. The complex (ppy)₂Ir(N- phenylmethacrylamide) (5), bearing an acryl

Full text of DOI:10.1021/om100714g

Organometallics 2011, 30, 77–83 77
DOI: 10.1021/om100714g
Amidate Iridium(III) Bis(2-pyridyl)phenyl Complexes: Application
Examples of Amidate Ancillary Ligands in Iridium(III)-Cyclometalated
Complexes
Wei Yang, Hao Fu, Qijun Song, Min Zhang,* and Yuqiang Ding*
School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi,
Jiangsu Province 214122, People’s Republic of China
Received July 21, 2010
The syntheses, structures, and photophysical properties of a series of iridium(III) bis(2-pyridyl)-
phenyl complexes, (ppy)2Ir(LX) (LX = amide ligands), are described. The complex (ppy)2Ir(N-
phenylmethacrylamide) (5), bearing an acrylamidate ligand, has been further employed for poly-
merization to generate the metal-containing homopolymer poly((ppy)2Ir(N-phenylmethacrylamide))
(6). In addition, the complexes (ppy)2Ir(acetylaniline) (2) and (ppy)2Ir(N-phenylbenzamide) (3) have
been structurally characterized by X-ray crystallography. It was found that the amidate ligand binds to
the Ir center in an imine/alkoxide mode via a four-membered, nearly planar ring (N-Ir-O-C); the
limited delocalization is supported by the lengthened C-O bond compared to the C-N bond
length in the amidate backbone and no strong absorption around 1650 cm-1 in the infrared spectra.
The photophysical and electrochemical properties of these complexes were then studied. The
maximum emission wavelengths ranging from 510 to 548 nm as well as the ΔEp values varying from
2.55 to 2.77 V can be attributed to the different effects of ancillary amide ligands tolerating different
electronic characters. The HOMO and LUMO energy levels and compositions of the iridium complexes
were investigated by DFT calculations. The amidate ancillary ligands affect the absorption and emission
energies of these complexes by tuning the HOMO energies.
Introduction
previously demonstrated that the cyclometalating ligands
(e.g., 2-phenylpyridine, 2-phenylquinoline) govern the emis-
sion color of the resulting complexes in comparison to the
ancillary ligands (e.g., acetylacetonate, picolinate).1a,3 How-
ever, this viewpoint has changed, since the emission colors
of Ir(dfppy)2(LX) (LX=ancillary ligand, dfppy=2-(4,6-
difluorophenyl)pyridyl) complexes can be tuned from blue to
red by modulating the ancillary ligand.4 Therefore, the design
and synthesis of both novel cyclometalating ligands and novel
ancillary ligands provide potential strategies for phospho-
rescence color tuning. However, the development of C∧Ns
(C∧N = cyclometalating ligand) has been hampered, since
the synthesis of dichloride-bridged (C∧N)2IrCl2Ir(C∧N)2 is
always difficult to achieve for steric and electronic reasons.4
Therefore, tuning the emission color by the ancillary ligand
structure in the heteroleptic iridium complex of the already
known cyclometalating ligand (C∧N) is considered a much
easier, efficient, and competitive approach. Over the past
few years, a number of contributions in the literature have
described a bidentate, anionic ancillary ligand (LX), such as
acetylacetonate (acac), functionalized β-diketonate, 2-pico-
linic acid, N-alkylsalicylimine,3a,5 pyrazolates, analogous tri-
azolates,6a-d and amidinate.6e,f However, the modification
of these ancillary ligands always requires complicated chem-
ical reactions, and most of them are coordinated to the Ir
atom via a five- or six-membered ring. Therefore, it is of great
Iridium(III)-cyclometalated complexes have attracted
considerable attention due to their unique photophysical pro-
perties and applications in organic light-emitting diodes
(OLEDs).1 These complexes can capture both singlet and
triplet excitons and greatly enhance the internal phospho-
rescence quantum efficiency of OLEDs toward 100%.2 It was
*To whom correspondence should be addressed. E-mail: yding@
jiangnan.edu.cn (Y.D.); zm31289@yahoo.com.cn (M.Z.).
(1) (a) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.
J. Am. Chem. Soc. 2001, 123, 4304–4312. (b) Tamayo, A. B.; Alleyne,
B. D.; Djurovich, P. I.; Lamansky, S.; Tsyba, I.; Ho, N. N.; Bau, R.;
Thompson, M. E. J. Am. Chem. Soc. 2003, 125, 7377–7387. (c) Polson,
M.; Fracasso, S.; Bertolasi, V.; Ravaglia, M.; Scandola, F. Inorg. Chem.
2004, 43, 1950–1956. (d) Muegge, B. D.; Richter, M. M. Anal. Chem. 2004,
76, 73–77. (e) You, Y.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438–
12439. (f) Hwang, F. M.; Chen, H. Y.; Chen, P. S.; Liu, C. S.; Chi, Y.; Shu,
C. F. Inorg. Chem. 2005, 44, 1344–1353. (g) Thomas, K. R. J.; Velusamy,
M.; Lin, J. T. Inorg. Chem. 2005, 44, 5677–5685. (h) Yang, C. H.; Cheng,
Y. M.; Chi, Y. Angew. Chem., Int. Ed. 2007, 46, 2418–2421.
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Heeger, A. J.; Bazan, G. C. Chem. Commun. 2002, 7, 784–785.
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r
2010 American Chemical Society
Published on Web 12/14/2010
pubs.acs.org/Organometallics

78 Organometallics, Vol. 30, No. 1, 2011
Yang et al.
Scheme 1. Synthesis of (ppy)2Ir(amidate) Complexesa
significance and interest to explore a new type of ancillary
ligand, which could not only be readily synthesized and
modified but also be coordinated to the Ir atom via a scarcely
cyclic delocalized model.
In the past several years, the subject of amide donors
serving as ligands in coordination chemistry has attracted
much attention for several reasons. (1) Amides can be easily
synthesized in high yields from readily available starting
materials. (2) Substituents on amide-based ligands can be
varied to regulate both electronic and steric features of the
resulting transition-metal complexes. (3) Binding modes to
the metal center are controllable via the mediation of N-donor
substituents or carbonyl-donor substituents on the amidate
ligands.7 To date, a number of organometallic amidate com-
plexes have been synthesized and structurally reported.7,8
Especially in recent years, complexes with Ti, Zr, Al, etc.
have been used by Schafer and other researchers to investi-
gate a wide range of applications, including reaction interme-
diates,8g catalysis for the hydroamination of alkynes8d,h,m
and alkenes8j,l and for the transamidation of unactivated
secondary carboxamides,8k and precursors for the polymer-
ization of polar monomers,8c to name but few. To the best of
our knowledge, there have been few reports, however, on the
a Legend: 2, R1 = CH3, R2 = Ph; 3, R1 = Ph, R2 = Ph; 4, R1 = Ph,
R2 = naphthyl; 5, R1 = isopropenyl, R2 = Ph.
use of amides to influence the photophysical properties of
metal complexes. It is noteworthy that amides exhibit ex-
cellent performance in many fields: polyamide (nylon), espe-
cially aromatic polyamide, has outstanding stability (high
melting point and decomposition temperature)9 and aryl-
amines are used as superlative organic electron transport
materials.10 Therefore, it is highly desirable to synthesize a
class of thermally stable four-membered-ring iridium(III)
complexes with excellent optical performance by employing
N-aryl-substituted amides as ligands. In this paper, we report
the first synthesis of amidate iridium(III) bis(2-pyridyl)phe-
nyl complexes.Crystal structure analysis, a density func-
tional theory (DFT) study, and measurement of electro-
chemical properties as well as photophysical properties for
these complexes have been carried out. The ultimate goal is
to investigate the influence of chelating amidate ligands on the
photophysical properties of these cyclometalated complexes.
(5) (a) Yang, C.; Li, S.; Chi, Y.; Cheng, Y.; Yeh, Y.; Chou, P.; Lee, G.;
Wang, C.; Shu, C. Inorg. Chem. 2005, 44, 7770–7780. (b) Kwon, T.; Cho,
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J. Organomet. Chem. 2009, 694, 3325–3330. (e) Ahn, S. Y.; Ha, Y. Mol.
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Results and Discussion
(6) (a) Song, Y.; Yeh, S.; Chen, C.; Chi, Y.; Liu, C.; Yu, J.; Hu, Y.;
Chou, P.; Peng, S.; Lee, G. Adv. Funct. Mater. 2004, 14, 1221–1226.
(b) Hwang, F.; Chen, H.; Chen, P.; Liu, C.; Chi, Y.; Shu, C.; Wu, F.; Chou, P.;
Peng, S.; Lee, G. Inorg. Chem. 2005, 44, 1344–1353. (c) Zhou, G.; Ho, C.;
Wong, W.; Wang, Q.; Ma, D.; Wang, L.; Lin, Z.; Marder, T. B.; Beeby, A.
Adv. Funct. Mater. 2008, 18, 499–511. (d) Zhou, G.; Wang, Q.; Ho, C.;
Wong, W.; Ma, D.; Wang, L.; Lin, Z. Chem. Asian J. 2008, 3, 1830–1841.
(e) Peng, T.; Bi, H.; Liu, Y.; Fan, Y.; Gao, H.; Wang, Y.; Hou, Z. J. Mater.
Chem. 2009, 19, 8072–8074. (f) Liu, Y.; Ye, K.; Fan, Y.; Song, W.; Wang, Y.;
Hou, Z. Chem. Commun. 2009, 3699–3701.
Synthesis of (ppy)2Ir(amidate) Complexes. Scheme 1 illus-
trates the chemical structure andsynthetic procedureofhetero-
leptic iridium (ppy)2Ir(amidate) complexes. The chloride-
bridged dimer (ppy)2Ir(μ-Cl)2Ir(ppy)2 (1) was synthesized
according to the procedure described in the literature.11
Treatment of 1 with 2.5 equiv of amide derivatives in
dichloromethane for 24 h in the presence of sodium metha-
nolate at ambient temperature afforded (ppy)2Ir(amidate)
complexes 2-5 in quantitative yields. Volatilization of the
organic solvent CH2Cl2/hexane resulted in (ppy)2Ir(amidate)
complexes as orange to yellow crystals of 2-5.
An example of homopolymerization of complex 5 is shown in
Scheme 2. The reaction was initiated by azobis(isobutyro-
nitrile) (AIBN), and the mixture was stirred in THF at 70 °C for
4 h. The polymeric product 6 was obtained by repetitive
precipitation with methanol.
Crystal Structures of 2 and 3. The molecular structure of 2,
determined by X-ray diffraction, is shown in Figure 1.
It reveals that the Ir atom is approximately octahedrally
coordinated to N-acetylaniline and two ppy ligands. The
coordinating configuration of the “(ppy)2Ir” fragment in
complex 2 is retained as that observed in the chloro-bridged
dimer (ppy)2Ir(μ-Cl)2Ir(ppy)2.11b The formation of N(3)∧O-
(1) coordinated to Ir(1) is a nearly planar configuration
(0.0193°); however, the benzene ring substituent on N(3)
(7) (a) Huang, Y.; Huang, B.; Ko, B.; Lin, C. Dalton Trans. 2001,
1359–1365. (b) Lee, A. V.; Schafer, L. L. Eur. J. Inorg. Chem. 2007, 16,
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Article
Organometallics, Vol. 30, No. 1, 2011 79
Figure 1. ORTEP diagram of 2 with thermal ellipsoids shown
at the 30% probability level. The hydrogen atoms have been
˚
omitted for clarity. Selected bond distances (A) and angles (deg):
Ir(1);N(1) = 1.999(1), Ir(1);N(2) = 2.016(1), Ir(1);N(3) =
2.146(1), Ir(1);C(11)=1.988(1), Ir(1);C(22)=1.940(1), Ir(1);
O(1)=2.266(7), C(24)-O(1)=1.322(2), N(3)-C(24)=1.273(2);
C(22)-Ir(1)-N(2)=79.0(5), N(3)-Ir(1)-O(1)=59.8(4), C(11)-
Ir(1)-N(1) = 80.5(5).
Figure 2. ORTEP diagram of 3 with thermal ellipsoids shown
at the 30% probability level. The hydrogen atoms have been
˚
omitted for clarity. Selected bond distances (A) and angles (deg):
Ir(1);N(1) = 2.027(4), Ir(1);N(2) = 2.008(5), Ir(1);N(3) =
2.155(4), Ir(1);C(11) = 1.977(5), Ir(1);C(22) = 2.026(4),
Ir(1);O(1)=2.272(3), C(23)-O(1)=1.261(6), N(3)-C(23)=
1.313(6); C(22)-Ir(1)-N(2) = 80.6(2), N(3)-Ir(1)-O(1) =
58.5(5), C(11)-Ir(1)-N(1) = 88.0(2).
Scheme 2. Synthesis of the Homopolymer poly[(ppy)2Ir-
(N-phenyl methacrylamide)] (6)
Table 1. Effect of the Concentration of Reactants on the
Molecular Weight
concn
of AIBN (mol/L)a
concn
of complex 5 (mol/L)b
103M
(g/mol)
entry
1
2
3
4
5
0.0396
0.0396
0.0396
0.0183
0.0609
0.038
0.075
0.100
0.038
0.038
6.07
9.32
15.40
8.90
5.78
a Concentration of AIBN; T = 343 K. b Concention of complex 5
[(ppy)2Ir(N-phenylmethacrylamide)]; T = 343K.
deviates from the plane of the four-membered ring at an
˚
angle of 31.3°. The bond length of Ir(1)-N(3) (2.146(1) A) is
˚
longer than those of Ir(1)-N(1) (1.999(1) A) and Ir(1)-N(2)
˚
(2.016(1) A), but all of these Ir-N bond lengths fall into the
range of reported data of Ir-N (1.982-2.189 A).1a,12,13 The
˚
˚
bond length of Ir(1)-O(1) (2.266(7) A) is much greater than
˚
the mean value of 2.088 A reported in the Cambridge Crys-
tallographic Database.14a In addition, the N(3)-Ir(1)-O(1)
angle (59.8(4)°) is found to be wider than the reported
value.8b
The molecular structures of complexes 2 and 3 are ap-
proximately similar. The bond lengths and angles of crystal-
line 3 differ slightly from those of crystalline 2 (Figures 1 and 2).
The four-membered ring N(3)-Ir(1)-O(1)-C(23) is nearly
planar (0.0291°), and the benzene groups on N(3) and C(23)
(12) Zhang, Y.; Baer, C. D.; Camaion, N. C.; O’Brien, P.; Sweigart,
D. A. Inorg. Chem. 1991, 30, 1685–1687.
(13) Neve, F.; Crispini, A.; Eur., J. Inorg. Chem. 2000, 1039–1043.
(14) (a) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.;
Kennard, O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith,
J. M.; Watson, D. G. J. Chem. Inf. Comput. Sci. 1991, 31, 187–204. (b)
Brown, C. J. Acta Crystallogr. 1966, 21, 442–455. (c) Hariharan, M.;
Srinivasan, R. Acta. Crystallogr., Sect. C 1990, 46, 1056–1058.
Figure 3. UV-vis absorption and normalized PL emission
spectra of complexes 2-6. The PL emission spectra are normal-
ized to the maximum peak of complex 6 (λ ∼517 nm). Measure-
ments for all the complexes have been carried out with CH2Cl2
solutions having a concentration of 10-5 mol/L.

80 Organometallics, Vol. 30, No. 1, 2011
Table 2. Photophysical Properties of Iridium Complexesa
Yang et al.
2
3
4
5
6
abs wavelength λ (nm)
soln luminescence λ (nm)
ΦPL
251, 297, 346, 442
510
0.060
250, 298, 370, 430
542
0.089
248, 261, 291, 370, 418
548
0.095
262, 298, 341, 404, 463
545
0.155
262, 297, 341, 402, 464
517
0.289
a Absorption and emission spectra were recorded in spectroscopic grade dichloromethane at 298 K. Quantum yields of emission were measured in
degassed dichloromethane solutions, using Alq3 in DMF (ΦPL = 0.116) as a reference.
Figure 4. Cyclic voltammograms of iridium complexes 2-5 (10-4 mol/L) with 0.1 mol/L of TBAPF6 at a scan rate of 100 mV/s. The
CV scans of all iridium complexes are single scans. All potentials were referenced to SCE.
Table 3. Electrochemical Data for Iridium Complexesa
deviate from the plane at angles of 44.9 and 45.0°, respec-
tively. In comparison to free amides (N-acetylaniline and
N-phenylbenzamide),14b,c the coordinating process in com-
plexes 2 and 3 significantly increases the bond length of C-O
while decreasing the C-N bond length in the amide simul-
taneously, which is the result of resonance of the electrons in
the chelating amidate ligand to Ir to form a four-membered
ring. The partial double bond feature increases the bond
length of the carbonyl group and decreases the length of the
C-N bond, which is consistent with the results of the
infrared (IR) spectra, which lack a strong absorption around
Ep (V)
complex
oxidn
redn
ΔEp (V)
2
3
4
5
1.52
1.47
1.46
1.47
-1.03
-1.12
-1.16
-1.30
2.55
2.59
2.62
2.77
a All electrochemical data were determined at room temperature in
CH3CN solution containing 0.1 mol/L TBAPF6.
1650 cm-1
.
of starting material 5 along with a relatively lower concen-
tration of AIBN favors the polymerization (Table 1, entries
1-5).
Photophysical Properties. The photophysical characteriza-
tion of (ppy)2Ir(amidate) complexes 2-6 was studied as
shown in Figure 3. All of these complexes give similar
The number-average molecular weight (M) of the homo-
polymer 6 was measured by gel permeation chromatography
(GPC), and the results are shown in Table 1. It is found that
the concentrations of complex 5 and initiator (AIBN) have a
significant influence on the M value; a higher concentration

Article
Organometallics, Vol. 30, No. 1, 2011 81
Table 4. HOMOs and LUMOs of the Iridium Complexesa
a All the isovalues for the MO plots are 0.02.
absorption and emission spectra. The maximum absorption
wavelengths of the complexes are observed at 251, 255, 250,
247, 262, and 262 nm, respectively (Table 2); intense bands
from 250 to 330 nm in the ultraviolet part of the absorption
spectra can be assigned to the spin-allowed ligand-centered
π-π* transitions of the C∧N ligands. The weak bands
observed between 330 and 430 nm can be attributed to the
1MLCT spin-allowed transitions. In addition, much weaker
bands are also observed beyond 400 nm due to the contribu-
tion of 3MLCT transitions.
Electrochemical Properties. Cyclic voltammetry (CV) was
employed to study the electrochemical properties of these
iridium complexes (Figure 4); the I-V response can provide
information on the kinetics of the electron-transfer reaction
and thermodynamics of the electrode-electrolyte interface.
The cyclic voltammograms of the (ppy)2Ir(amidate) complexes
are shown in Figure 4, at a Pt-disk working electrode in
CH3CN solution (10-4 mol/L) with 0.1 mol/L tetrabutylam-
monium hexafluorophosphate (TBAPF6) as the supporting
electrolyte. The relevant oxidation and reduction potentials
are given in Table 3.
All of the (ppy)2Ir(amidate) complexes 2-6 reported here
give phosphorescence quantum yields (ΦPL) between 0.060
and 0.289 (Table 2). Complex 6 shows the highest ΦPL value,
which is lower than that of (ppy)2Ir(acac).3a The wavelengths
of solution photoluminescence (PL) of complexes 2-6 are
observed around 520 nm, which fall into the green light
region. These wavelengths of solution PL are very similar to
those for (ppy)2Ir(acac).3a It is found that when unsaturated
C-C substituents on the nitrogen atom or carbonyl group of
the amidate ligand are increased, the maximum emission
wavelengths of these complexes undergo a red shift (Table 2).
In comparison to complex 5, the emission spectrum of poly-
meric complex 6 exhibits an obvious hypsochromic shift and a
significant increase in the absorption intensity. The blue shift
in the emission spectra can be attributed to the results of
substituent modification: the vinyl group was transformed
into an alkyl group on the amidate ligand after polymeriza-
tion occurred. Furthermore, the polymerization affords the
higher molecular weight complex 6, which contains more
fluorophores at the same concentration and could result in
stronger emission intensity.
The oxidation process in the CV of 2-5 in CH3CN is
assigned to the Ir(III)/Ir(IV) couple. The first oxidation
peaks of Ep for complexes 2-5 are observed at 1.52, 1.47,
1.46, and 1.47 V, respectively (Table 3). These close oxida-
tion potentials obtained under identical conditions indicate
that an increase in the number of conjugated double bonds
does not affect the oxidative process of the iridium complexes
very much. The first reduction peaks of these complexes appear
at Ep -1.03, -1.12, -1.16, and -1.30 V, respectively. The
reductive process is caused by the reduction of the amidate
ancillary ligands, and the reduction potentials have no relation
to the length of the conjugated system; the different Ep values
are assigned to the different electrochemical environments of
the amides.
DFT Calculations. DFT calculations for complexes 2-5
were further carried out to ascertain the influence of the
amide ligands on the photophysical properties. The highest
occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) energy levels and compositions
of the four iridium complexes were analyzed, and the results

82 Organometallics, Vol. 30, No. 1, 2011
Table 5. Frontier Orbital Compositions (%) of Four Iridium Complexes from DFT
Yang et al.
MOs
2
3
4
5
HOMO
40.62 (ppy)
50.35 (Ir)
37.60 (ppy)
48.22 (Ir)
36.14 (ppy)
45.91 (Ir)
38.24 (ppy)
48.21 (Ir)
9.03 (acetylaniline)
92.21 (ppy)
5.14 (Ir)
14.18 (N-phenylbenzamide)
90.63 (ppy)
4.86 (Ir)
17.95 (N-naphthylbenzamide)
89.52 (ppy)
4.85 (Ir)
13.55 (N-phenylmethacrylamide)
91.05 (ppy)
4.99 (Ir)
LUMO
2.65 (acetylaniline)
4.51 (N-phenylbenzamide)
5.63 (N-naphthylbenzamide)
3.96 (N-phenylmethacrylamide)
ar given in Tables 4 and 5. The HOMO energy levels vary
from -4.89 to -4.82 eV, while the LUMO energy levels are
very close, with energies ranging from -1.40 to -1.44 eV.
The LUMO distributions of 2-5 primarily reside on cyclo-
metalated ligands (ppy) in comparison to the metal center
and amidate ancillary ligands, which is similar to the case for
the reported iridium analogues.15 The electronic populations
confined to the metallic d orbital and ppy in the HOMOs of
2-5 are about 48% and 38%, repectively. However, the
contribution of the amidate ligand is early 17.95% (Table 5),
quite different from that of the complex of (ppy)2Ir(acac), in
which the contribution of the ancillary ligand (acac) is almost
negligible.15 These results can be ascribed to the far better
partial p-bonding ability to the metal center of the amide
ligands in comparison to that of the acac ligand. On the basis
of these results obtained by DFT, the amidate ancillary ligands
could also influence the energy of the HOMO in (C∧N)2Ir(LX)
complexes, which is quite consistent with reported results.16
The chloro-bridged dimer (ppy)2Ir(μ-Cl)2Ir(ppy)2 was synthe-
sized via the described procedure.11
General Experiments. All of the synthetic procedures invol-
ving Ir(III) species and sodium methanolate were carried out
under a dry argon or nitrogen atmosphere by using a standard
Schlenk tube; the main concern is the oxidative stability of
intermediate complexes and moisture-sensitive sodium metha-
nolate used in the reactions.
Synthesis of (ppy)2Ir(amidate) Complexes 2-5. Complexes
2-5 were prepared via identical procedures. Herein, a typical
procedure for the synthesis of (ppy)2Ir(acetylaniline) (2) is
described as follows.
[(ppy)2IrCl]2 (0.107 g, 0.10 mmol) and acetylaniline (0.037 g,
0.25 mmol) were dissolved in dichloromethane (10 mL); sodium
methanolate (0.054 g, 1.0 mmol) was then added to the mixture
to neutralize the hydrochloric acid generated by the reaction.
The resulting mixture was stirred at room temperature for 24 h
and was then taken to dryness in vacuo, and the residue was
washed with water and diethyl ether successively to afford the
yellow crude product, which was further recrystallized in CH2Cl2/
petroleum ether, and the desired yellow crystalline product 2 was
obtained in 62% yield (0.078 g). IR (KBr): 3053 m, 2961 w, 2926 w,
1635 w, 1604 s, 1582 s, 1544 m, 1519 s, 1453 s, 1439 s, 1411 s, 1305
m, 1264 m, 1226 m, 1159 m, 1059 m, 1030 m, 1007 m, 964 m, 756
Conclusions
In summary, we have successfully prepared and character-
ized a series of iridium complexes containing amidate ancil-
lary ligands. X-ray crystallographic studies have been carried
out for complexes 2 and 3. The high concentration of
complex 5 and relatively low concentration of initiator favor
polymerization and yield a higher molecular weight product.
The electrochemical properties are influenced by the substit-
uents on the amidate ancillary ligands. The emission spectra
of complexes 2-6 are different, while their maximum ab-
sorption wavelengths are similar. The HOMO and LUMO
energy levels and compositions of complexes 2-5 were inves-
tigated by DFT calculations. The results indicate the energy
of the HOMOs of (C∧N)2Ir(LX) complexes could also be
significantly influenced by amidate ancillary ligands. Thus, a
color-tuning strategy can be achieved by mediating the sub-
stituents on the nitrogen atom or carbonyl group of the
amidate ligands.
1
s, 732 m, 697 m, 670 m. H NMR (in CDCl3): δ 2.17 (s, 3H),
6.17 (d, J=8 Hz, 2H), 6.52 (d, J=11.2 Hz, 2H), 6.60 (t, J=
7.6 Hz, 1H), 6.69 (t, J=7.4 Hz, 1H), 6.77 (t, J=7.6 Hz, 1H),
6.84 (dd, J=7.6, 7.2 Hz, 2H), 7.02 (t, J=7.6 Hz, 2H), 7.17 (t,
J = 6.4 Hz, 2H), 7.52 (dd, J = 7.6,7.2 Hz, 2H), 7.80 (t, J =
7.4 Hz, 2H), 7.92 (d, J=7.6 Hz, 2H), 8.80 (d, J=7.2 Hz, 1H),
8.89 (d, J=7.2 Hz, 1H). Anal. Found: C, 56.71; H, 3.86; N, 6.58.
Calcd: C, 56.77; H, 3.81; N, 6.62.
(ppy)2Ir(N-phenylbenzamide) (3). Orange-yellow crystal, yield
0.098 g (70%). IR (KBr): 3057 m, 1653 w, 1605 s, 1581 s, 1560 w,
1519 s, 1477 s, 1438 m, 1417 s, 1316 m, 1267 m, 1226 m, 1160 m,
1125 m, 1060 m, 1030 m, 932 m, 793 m, 755 m, 734 m, 695 m, 630 w,
612 w. 1H NMR (in CDCl3): δ 6.21 (d, J=7.6 Hz, 2H), 6.44 (d,
J=7.6 Hz, 2H), 6.65 (t, J=7.6 Hz, 1H), 6.71 (t, J=7.2 Hz, 2H),
6.79 (t, J=10 Hz, 2H), 6.88 (m, 2H), 7.14 (t, J=7.6 Hz, 2H),
7.22 (t, J = 7.2 Hz, 1H), 7.34 (d, J = 8.0 Hz, 1H), 7.47 (d,
J=7.6 Hz, 2H), 7.51 (dd, J=7.4, 7.2 Hz, 2H), 7.76 (dd, J = 7.6,
7.2 Hz, 2H), 7.82 (m, 3H), 8.91 (d, J = 7.2 Hz, 1H), 8.96 (d,
J=7.6 Hz, 1H). Anal. Found: C, 60.21; H, 3.88; N, 6.09. Calcd:
C, 60.33; H, 3.76; N, 6.03.
(ppy)2Ir(N-naphthylbenzamide) (4). Orange-yellow crystal,
yield 0.107 g (72%). IR (KBr): 3055 m, 1644 w, 1606 s, 1582 s,
1524 s, 1478 s, 1437 m, 1417 s, 1301 m, 1269 m, 1228 m, 1160 m,
1061 m, 1030 m, 916 m, 791 m, 755 m, 733 m, 695 m, 630 w, 612 w.
1H NMR (in CDCl3): δ 6.04 (d, J = 8 Hz, 1H), 6.21 (d, J =
3.6 Hz, 1H), 6.37 (t, J = 7.6 Hz, 1H), 6.59 (d, J = 7.6 Hz, 1H),
6.64 (m, J = 7.2 Hz, 2H), 6.82 (t, J = 7.6 Hz, 2H), 7.05 (m, 3H),
7.12 (t, J = 7.6 Hz, 1H), 7.22 (t, J = 7.4 Hz, 2H), 7.31 (d, J =
7.2 Hz, 1H), 7.37 (d, J = 7.6 Hz, 1H), 7.45 (d, J = 7.6 Hz, 1H),
7.57 (m, 3H), 7.74 (m, 3H), 7.92 (t, J = 7.6 Hz, 3H), 9.06 (d, J =
7.6 Hz, 1H), 9.12 (d, J = 7.2 Hz, 1H). Anal. Found: C, 62.59; H,
3.91; N, 5.59. Calcd: C, 62.72; H, 3.78; N, 5.63.
Experimental Section
Materials. IrCl3 3H2O, acetylaniline, and other chemicals
3
were obtained from commercial sources and used without
further purification. All solvents were dried by common methods
and freshly distilled prior to use. Amide derivatives (N-phenyl-
benzamide,17 N-naphthylbenzamide,18 N-phenylmethacrylamide19)
were prepared according to the reported literature procedures.
(15) Hay, P. J. J. Phys. Chem. A 2002, 106, 1634–1641.
(16) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho,
N. N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg.
Chem. 2005, 44, 1713–1727.
(17) Vogel, A. I. Elementary Practical Organic Chemistry; Longmans,
Green: London, New York, Toronto, 1959; p 243.
(18) DeRuiter, J.; Swearingen, B. E.; Wandrekar, V.; Mayfield, C. A.
J. Med. Chem. 1989, 32, 1033–1038.
(19) Wang, W.; Zhu, T.; Chen, G.; Li, C.; Di, H.; Ren, C.; Ding, Y.
Synth. Met. 2008, 158, 1022–1027.
(ppy)2Ir(N-phenylmethacrylamide) 5. Orange crystal, yield
0.093 g (62%). IR (KBr): 3057 m, 1604 s, 1581 s, 1534 s, 1475 s,
1438 m, 1420 s, 1267 m, 1225 m, 1160 m, 1060 m, 1029 m, 929 m,
791 m, 755 m, 734 m, 694 m, 629 w. 1H NMR (in CDCl3):

Article
Organometallics, Vol. 30, No. 1, 2011 83
δ 2.09 (s, 3H), 5.29 (s, 1H), 5.83 (s, 1H), 5.90 (d, J = 8 Hz, 2H),
6.52 (m, 2H), 6.72 (m, 4H), 7.02 (m, 2H), 7.45 (d, J = 7.6 Hz,
2H), 7.50-7.70 (m, 3H), 7.78 (d, J = 8 Hz, 2H), 7.85 (d, J =
7.2 Hz, 2H), 8.88 (d, J = 7.6 Hz, 2H). Anal. Found: C, 58.08; N,
6.36; H, 3.84. Calcd: C, 58.16; N, 6.46; H, 3.97.
Characterization Methods. IR spectra were recorded on a
FTLA2000 spectrometer by dispersing samples in potassium
bromide. NMR spectra were collected on a Bruker ACF-400
spectrometer with deuterated chloroform as solvent and tetra-
methylsilane as internal standard. Absorption spectra were
measured using a UV/vis spectrophotometer (Model TU-1901).
PL spectra were obtained using an RF-5301PC spectrofluorimeter
(Shimadzu, Japan) connected to a photomultiplier tube with a
xenon lamp as the excitation source. The PL quantum yields
were measured in degassed dichloromethane solutions, using
Synthesis of Polymer 6. AIBN (0.03 g, 0.2 mmol) and 5 (0.10 g,
0.15 mmol) were dissolved in THF (4 mL) in a round-bottom
flask; the resulting mixture was stirred at 70 °C for 48 h. After the
mixture was cooled to room temperature, methanol (100 mL) was
added to precipitate the polymeric product. The crude product
was obtained after filtration. Then it was further dissolved in
THF (4 mL); the subsequent addition of methanol (100 mL)
gave a deep yellow precipitate, which was then filtered and dried
under reduced pressure to afforded the desired product 6 (yield
56%). The M value of the homopolymer 6 was measured by GPC.
Theoretical Calculations. Calculations on the electronic
ground state of the complexes were performed using B3LYP
density functional theory.20 A 6-31G basis set was implemented
for the first- and second-row elements H, C, N, and O, whereas
the LANL2DZ basis set was employed for Ir. Ground-state
B3LYP calculations were carried out using the Gaussian 03 suite
of programs.21
tris(8-hydroxyquinoline)aluminum (Alq3) in DMF (ΦPL
=
0.116)22 as a reference. The electrochemical properties of the
Ir(III) complexes were examined by CV and measured by
using a standard one-compartment, three-electrode electrochem-
ical cell in an IM6e electrochemical worksation (ZAHNER
elektrik, Germany). A Pt-disk electrode was used as the working
electrode, a Pt wire as the counter electrode, and a saturated
calomel electrode (SCE) as the reference electrode. Molecular
weights of polymers were measured by a GPC (Waters 1515)
using N,N-dimethylformamide as a solvent and calibrated
against polystyrene standards. X-ray data for compounds 2
and 3 were collected using a Bruker SMART APEX II
CCD area detector using monochromated Mo KR radiation
˚
(λ = 0.710 73 A). Crystal data of 2 and 3 were measured at
(20) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789.
(b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
293(2) K.
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Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A. J.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V.G.;Dapprich,S.;Daniels,A.D.;Strain,M.C.;Farkas,O.;Malick,D.K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople,
J. A. Gaussian 03, revision E.01; Gaussian, Inc., Wallingford, CT, 2004.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China (Nos.
20571033 and 20971058) and by the Program for New
Century Excellent Talents in University (NCET-06-0483).
Supporting Information Available: CIF files giving crystal-
lographic data for 2 and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
(22) Lytle, F. E.; Story, D. R.; Juricich, M. E. Spectrochim. Acta, Part
A 1973, 29, 1357–1369.